Why is the figure so much more definitive? The Census Bureau figures released today that I’ve cited above come from the American Community Survey (ACS), which is based on a survey of about 3.5 million households (about 8.8 million people). In contrast, the NHIS surveys only 87,500 people and all the other surveys focus exclusively on adults, hence cannot provide an accurate population-wide estimate of changes in the number of uninsured. Moreover, these private surveys also are considerably smaller: Gallup surveys less than 44,000 adults 18 and over, Urban Institute samples about 7,500 non-elderly adults, Commonwealth Surveys less than 6,200 non-elderly adults and RAND surveys less than 2,500 non-elderly adults.